Thermoanalytical and spectroscopic studies on hydrazinium lighter lanthanide complexes of 2-pyrazinecarboxylic acid

The new hydrazinium lanthanide metal complexes of 2-pyrazinecarboxylic acid (HpyzCOO) of the formulae (N₂H₅)₂[Ln(pyzCOO)₅] · 2H₂O (1), where Ln = La or Ce and (N₂H₅)₃[Ln(pyzCOO)₄(H₂O)] · 2NO₃ (2), where Ln = Pr, Nd, Sm or Dy have been synthesized and characterized by physico-chemical methods. The IR absorption bands of N–N stretching at 960 cm⁻¹ unambiguously prove the existence of N₂H₅ ⁺ ions. The bonding parameters β, b^1/2, % δ and η, have been calculated from the electronic spectroscopic (hypersensitive) bands of Pr(III) and Nd(III) complexes. All the complexes undergo endothermic followed by exothermic decomposition to leave the respective metal oxides as the end products. However, the DTA of the complexes 2 demonstrate rather sharp peak than the complexes 1, owing to overwhelming exothermicity, which may be due to the loss of both hydrazine and nitrate moieties in the same step. The X-ray powder diffraction studies reveal the existence of isomorphism among the member complexes.     

Thermoanalytical and mössbauer spectroscopic studies of phase transformations of amorphous chromium hydroxide

To establish the structures of the phase transformation products of amorphous chromium hydroxide and the region of their stability, the thermally initiated transformations were studied at normal and reduced pressure (0.133 Pa) by differential thermal analysis, Mössbauer spectroscopy (on admixed⁵⁷Fe atoms) and X-ray diffraction phase analysis.At reduced pressure the region of stability of amorphous chromium oxide formed during hydroxide dehydration is wider.The Mössbauer shift of admixed⁵⁷Fe atoms in amorphous chromium hydroxide is characteristic of Fe³⁺, but the magnitude of the quadrupole splitting considerably exceeds those for simple and compound iron oxides and oxide-hydroxides. From this, it can be concluded that the symmetry of the local environment of the chromium atoms in amorphous chromium hydroxide is anomalously low.

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Zusammenfassung Um die Struktur der Umwandlungsprodukte des amorphen Chrom(III)-oxids und seinen Existenzbereich zu ermitteln, wurden die thermischen Umwandlungen bei normalem und vermindertem Druck (0,133 Pa) durch DTA, Mössbauer-Spektroskopie (an zugesetzten⁵⁷Fe-Atomen) und Röntgenbeugungs-Phasenanalyse untersucht. Unter vermindertem Druck wird der Stabilitätsbereich des bei der Entwässerung des Hydroxids gebildeten amorphen Chrom(III)-oxids erweitert. Die Mössbauer-Verschiebung von zugesetzten⁵⁷Fe-Atomen in amorphem Chrom(III)-oxid ist charakteristisch für Fe³⁺, die Quadrupol-Aufspaltung übertrifft die für einfache und komplexe Eisenoxide und -oxid-hydroxide beträchtlich. Daraus wird geschlossen, dass die Symmetrie der Umgebung der Chromatome im amorphen Chrom(III)-oxid ungewöhnlich niedrig ist.

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, (0.133 ) , ⁵⁷Fe . , . ⁵⁷Fe Fe³⁺, - . .

     

Thermoanalytical studies on lobster shell

Chromium(III) oxide reverses the sequence of dehydration of barium perchlorate trihydrate (BP). Between 223 and 310? the oxide reacts with anhydrous BP in a 1∶1 molar ratio to give the yellow barium dichromite BaCr₂O₄. Between 350 and 430? this material reacts in 1∶1 stoichiometry with BP, to give barium chromate BaCrO₄. The products have been identified by X-ray diffraction analysis. The formation of an unkown phase is also reported.     

Thermoanalytical studies on lobster shell

The chemical composition of lobster shells was determined by thermal analysis without previous sample preparation. The humidity and ash content were directly calculated from the TG curve. A correlation between the percentage weight loss is a particular temperature interval and the concentration of chitin and protein in the starting material was found, and based on this new method is proposed for the quantitative determination of both polymers. The residual protein after the deproteinization could be estimated with 0.3% error.

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Zusammenfassung Mittels Thermoanalyse wurde ohne Probenaufbereitung die chemische Zusammensetzung von Hummerpanzern ermittelt. Feuchtigkeits- und Aschegehalt wurden aus der TG-Kurve direkt berechnet. Es konnte ein Zusammenhang zwischen der prozentuellen Massenabnahme in einem bestimmten Temperaturintervall und der Konzentration von Chitin und Protein in der Ausgangssubstanz ermittelt und auf dieser Grundlage ein neues Verfahren zur quantitativen Bestimmung beider Polymere vorgeschlagen werden. Das nach der Deproteinierung verbleibende Protein konnte mit einem relativen Fehler von 0.3 % bestimmt werden.

     

Thermoanalytical studies on montmorillonite-pirimicarb complexes

The thermal decomposition of the interlayer complexes of homoionic samples of montmorillonite with the carbamate insecticide pirimicarb (2-dimethylamino-5, 6-dimethyl pyrimidin 4-yl-dimethyl carbamate) was studied using TG and DSC techniques. The decomposition of the organic compound was followed by IR spectroscopy and X-ray diffraction. It was observed that the thermal decomposition of pirimicarb is catalyzed by adsorption by the clay. Both the catalytic capacity of the clay and the values of the decomposition enthalpies depend on the characteristics of the interlayer cation of the montmorillonite.     

Thermoanalytical studies on hydrated tricalcium silicate

The thermal decomposition of the hydration products of tricalcium silicate has been studied by TG, DTG and DTA. The thermal decomposition characteristics of the CSH-phase formed changed, as the hydration progressed. The heat requirement for thermal decomposition of the calcium hydroxide formed in the hydration process was lower than the one of a pure crystalline material.     

Thermoanalytical studies of intumescent systems

Fire retardant intumescent coatings which produce a swollen char on heating are being frequently used to protect buildings containing structural steel from the effects of exposure to high temperatures caused by fire. This paper contains details of a study carried out using thermal analysis techniques to elucidate the mechanisms of the development of intumescent chars during the heating of an intumescent coating system based on ammonium polyphosphate, pentaerythritol and melamine. In particular, the role of melamine as the spumific agent has been studied. The melamine is shown to react chemically with the ammonium polyphosphate in addition to carrying out its role as the spumific, or blowing agent.     

Thermoanalytical studies of pitch pyrolysis

Characterization of pitches by thermal analysis techniques is highly relevant to the practical use of these materials, as they undergo heat treatments in all of their utilization processes. The aim of this work was to improve the interpretation of the complex DTA curves of pitches by comparison with model compounds. For this, TG/DTG/DTA was used to study under identical conditions the pyrolysis of a petroleum pitch and a coal tar pitch as well as a number of polycyclic aromatic hydrocarbons. Results were interpreted as a function of the molecular structure, pyrolysis reactivity and graphitizability of cokes from the hydrocarbons. It is concluded that condensation and polymerization, which are the most likely exothermal reactions predominant in petroleum pitches, indicate the presence therein of reactive molecules. Alternatively, endothermal phenomena such as distillation, depolymerization and cracking, predominant in coal tar pitches, suggest the presence of light, little reactive aromatic molecules.Financial support from DGICYT (project PB87-0456) is gratefully acknowledged.     

Thermoanalytical studies on specialty polymers in Japan

Thermoanalytical studies on specialty polymers in Japan are reviewed. The basic and applied researches for the developments of new specialty polymers such as high-performance polymers, liquid crystalline polymers, and biodegradable polymers during the 1990's are introduced from the standpoint of thermal analysis. Many studies were performed for the improvements of durability and thermal stability of engineering polymers, biodegradable polymers and so on. A special topic of researches on the thermal behavior of polymers by high-pressure differential thermal analysis is included in this review. This revised version was published online in July 2006 with corrections to the Cover Date.     

Thermoanalytical studies of some sweeteners

The thermal decomposition behavior of acesulfame-K (ACK), aspartame (ASP), sodium cyclamate (SCL), saccharine (SAC), and sodium saccharine (SSA) were investigated. After re-crystallization of the commercial samples the compounds were characterized by using elemental analysis, IR spectroscopy and thermoanalytical techniques (TG/DTG, DTA, and DSC). Evidences of hydrate water loss were observed for SSA and ASP. Melting was detected for SSA and SAC. Each compound decomposed in a characteristics way. The decomposition of APS and SAC took place completely, while ACK, SCL and SSA resulted in K₂SO₄, Na₂SO₄, and Na₂SO₄, as residues respectively. The Flynn-Wall-Ozawa method for kinetic calculations was applied for the volatilization of saccharine resulting in E _a = 80 ± 1 kJ mol⁻¹ and log A = 7.36 ± 0.07 min⁻¹.     

Thermoanalytical studies of imidazole-substituted coordination compounds

Four manganese(II) coordination compounds with bis(1-methylimidazol-2-yl)ketone (BIK) of general formula Mn(BIK)₂X₂ (X = Cl, Br, NO₃, ClO₄) were synthesized and characterized by elemental analysis, by UV–vis, and FTIR spectroscopies to be compared with the literature data. Following our previous thermoanalytical studies on imidazole-substituted coordination compounds, the thermal behavior of the synthesized Mn(II) complexes was investigated using TG and DTG techniques: the thermal profile is characterized by three substantial consecutive releasing steps for all the three complexes and the releasing supposed behavior is confirmed by EGA analysis performed by coupling the TG analyzer to an MS spectrometer. In particular, the first step is ascribed to the release of the two anions, followed by the loss of four methyl groups (side chains of the ligand) and two bridge-carbonyl groups. The residual tetra-imidazole manganese compound decomposes in a final step to give MnO as the final residue. Both the initial decomposition temperatures and the kinetic rate constants associated to the first decomposition step indicated a higher stability of the Mn(BIK)₂Cl₂ complex, the bromide complex being very close to the chloride one (first-step thermal stability: ClO₄ ⁻ <NO₃ ⁻ ≤Br⁻ <Cl⁻). Finally, the three-dimensional diffusion reaction model (D3) was selected to describe the first decomposition step for all the four complexes examined.     

Thermoanalytical studies on complexes of clotrimazole with cyclodextrins

γ-Cyclodextrin and dimethyl-β-cyclodextrin were used as solubilizing agents for a very poorly water-soluble drug, an imidazole derivative antifungal agent, clotrimazole; with the aim of improving the physicochemical properties of the drug. Solid products were prepared by physical mixing, kneading, precipitation and spray-drying methods in 1:1 and 1:2 drug:cyclodextrin molar ratios. Drug interactions were studied by thermoanalytical methods such as DSC, DTA, TG and DTG, X-ray diffractometry and Fourier transformation-infrared spectroscopy. The results demonstrated the formation of inclusion complexes in some products. This revised version was published online in July 2006 with corrections to the Cover Date.     

Thermoanalytical studies on protein-polysaccharide complexes of connective tissues

The Derivatograph has been found to be suitable for the investigation of biopolymers. consisting of polysaccharides and proteins. It could be demonstrated that interactions between the macromolecules of the collagen-proteoglycan-glycoprotein complexes significantly influence the thermal stability of the individual components.     

Thermoanalytical studies of hydrazidocarbonic acid derivatives

Preparation, thermal analysis and IR spectra of a number of transition metal hydrazidocarbonates have been described. Metal hydrazido carbonates decompose exothermically through oxalate and carbonate intermediates to the respective metal oxides. Reaction of ammonium carbonate with hydrazine hydrate yields hydrazinium derivative of hydrazidocarbonic acid; N₂H₃COON₂H₅.     

Thermoanalytical studies on complexes of ketoconazole with cyclodextrin derivatives

Inclusion complexation between cyclodextrin derivatives (hydroxypropyl-β-cyclodextrin and methyl-β-cyclodextrin) and a very poorly water-soluble antifungal agent, ketoconazole, was studied. Solid products were prepared by physical mixing, kneading and spray-drying methods in four molecular ratios: 2:1, 1:1, 1:2 and 1:3. The possibility of complex formation between the drug and the cyclodextrins was studied by thermal analysis. Supplementary techniques, such as X-ray diffractometry and Fourier transformation-infrared spectroscopy, were also applied to interpret the results of the thermal study of the products. This revised version was published online in July 2006 with corrections to the Cover Date.     

Thermoanalytical studies on cation distribution in submicronic titanomagnetites

Non-isothermal and isothermal TG studies on the cation distribution in submicronic titanomagnetites; Fe_3–xTi_xO₄ with 02O₃. The DTA results show that the temperature of oxidation of Fe²⁺ to Fe³⁺ ions is increased, whereas the temperature of phase change is decreased with increasing titanium substitution. The kinetics of oxidation is found to be governed by the law of diffusion for variable working conditions and for different extents of the vacancies created at the solid-gas interface. The diffusion of iron(II) ions located at octahedral sites proceeds with a lower activation energy than that of iron(II) ions located at tetrahedral sites. Diffusion rates were discerned to be composition-dependent and the variations can be identified with the distribution of the iron ions in sublattices.

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Zusammenfassung Es wird über nicht-isotherme und isotherme TG-Untersuchungen der Kationenverteilung in submikronen Titanomagnetiten (Fe_3–x Ti _x O₄ mit 0<x<0.82) berichtet. Titanomagnetite mitx<0.61 konnten unter 500° zu Titan-substituierten Magnetiten oxydiert werden, die eine größere Leerstellenkonzentration als-Fe₂O₃ aufweisen. Die DTA-Ergebnisse zeigen, daß die zur Oxydation von Fe²⁺- zu Fe³⁺-Ionen notwendige Temperatur mit zunehmender Titansubstitution ansteigt, die Phasenübergangstemperatur dagegen absinkt. Die Kinetik der Oxydation ist unter verschiedenen Arbeitsbedingungen und bei unterschiedlichen Konzentrationen der an der Fest-Gas-Grenzfläche gebildeten Fehlstellen diffusionsbestimmt. Die Aktivierungsenergie der Diffusion von an den oktaedrischen Stellen lokalisierten Fe(II)-Ionen ist geringer als die von tetraedrisch koordinierten Fe(II)-Ionen. Diffusionsgeschwindigkeiten werden als von der Konzentration abhängig erkannt und die Variationen können mit der Verteilung der Eisenionen im Subgitter identifiziert werden.

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Fe_3–x Ti _x O₄ c 0<x<0.82. x< 0.61 500° , -Fe₂O₃. , , . , — . , , . , .

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Paper presented at the World Conference on Thermal Analysis, Madeira (Portugal), 1986.     

Thermoanalytical studies of substances liberating aggressive gases

A modification to the derivatograph has been designed that allows thermoanalytical investigations of chemical compounds, including sulphides and acids, that evolve aggressive gases such as CO, SO₂, S, etc. during warming. Application of this modification is exemplified by studies on the thermal dehydrogenation of titanium hydride (TiH_1.85) and on the interaction of rhenium disulphide (ReS₂) with concentrated sulphuric acid.

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Zusammenfassung Es wird über die Modifizierung eines Derivatografen berichtet, die die Thermoanalyse von Stoffen ermöglicht, die wie z. B. Sulfide oder Säuren beim Erhitzen aggressive Gase wie z. B. CO, SO₂, S usw. freisetzen. Als Beispiel für die Anwendung dieser Modifizierung dienten Untersuchungen der thermischen Dehydrogenierung von Titanhydrid (TiH_1.85) und des Einwirkens von konzentrierter Schwefelsäure auf Rheniumsulfid (ReS₂).

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, , , , , SO₂, S . . 2- , - (³_1,85) (ReS₂) (H₂SO₄).

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Presented as a poster at ESTAC-4, Jena, GDR, 1987.     

Thermoanalytical studies of the pyrolysis of organic polymers

Some applications of thermoanalytical techniques (TG and DTA) to the study of organic polymer pyrolysis are described. It is shown that in order to obtain meaningful kinetic parameters strict control of environmental conditions is required. Experimental results are given for selected ethylene-propylene co- and ter-polymers, for halogenated polymers including polyvinyl chloride and neoprene in admixture with ferric oxide, and for other materials.     

Resonance Raman and infrared spectroscopic studies of high-output forms of human soluble guanylyl cyclase

The allosteric regulator BAY-41-2272 converts the CO adduct of soluble guanylyl cyclase (CO-sGC) enzyme from a low- to high-output form, with respect to production of cGMP. Resonance Raman (RR) and Fourier Transform Infrared (FTIR) spectroscopic techniques are used to show that the CO-sGC exists as major and minor conformers, both having nu(Fe-CO) and nu(C-O) modes characteristic of 6-coordinate species. It is further shown that addition of BAY-41-2272 to the CO adduct induces the transition of some fraction of the initial CO-heme adducts into two new CO-heme complexes, the fractional conversion being dependent on the temperature. One new complex displays vibrational modes characteristic of pentacoordinated CO-adduct, and its formation is not affected by temperature. The second complex, although slightly different from the original CO-adducts, is hexacoordinated, and its formation is facilitated by temperature. The production of substantial amounts of the 5-coordinate CO adduct upon addition of BAY-41-2272, reveals the fact that several out-of-plane heme deformation modes are simultaneously activated, an observation similar to that realized upon NO activation. While the precise nature of these modes will require elucidation by isotopic labeling experiments, by analogy with earlier studies of other heme proteins, several bands associated with modes attributable to peripheral substituent deformations and methine carbon movements are implicated. The documented formation of two new forms upon addition of Bay-41-2272 (a 5-coordinate and a new 6-coordinate form) is discussed with respect to the implications for enzyme activation.